The engineering design of landing gear for commercial aircraft presents many challenges. The landing gear is attached to the primary structure of the aircraft, and supports the entire weight of the aircraft during landing and ground operations. The landing gear must withstand the recurring transient forces associated with taking off and in particular, landing. Very high forces may be incurred in “hard landings,” for example, when the aircraft approaches the ground with a greater-than-planned vertical velocity. Hard landings may result from adverse weather conditions, mechanical issues, pilot error, or the like. During flight the landing gear is subjected to continuous shaking and vibrational forces. During ground operations the landing gear may also be engaged for towing the aircraft to and from locations at the terminal.
To decrease drag and improve performance of an aircraft, the landing gear in most commercial aircraft are articulated and configured to retract into a landing gear bay in the body or wing of the aircraft during flight. Retractable landing gear must be able to readily retract into the landing gear bay, and reliably deploy to a locked position upon approach to the desired destination. Retractable landing gear typically includes one or more folding stays (also called struts) which may include associated downlock actuators. The stays deploy to securely lock the landing gear in the deployed position. For example, a side stay provides support against side loads. A drag strut provides support against fore and aft loads.